Logic, Argument and
Medicine
Sanjay Modgil
Advanced Computation Lab
Cancer Research UK
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Logic, Argument and
Medicine
Logic based reasoning in Medical AI systems
Logic and Argumentation
• Argumentation based reasoning: decision making,
deliberation…
• Communication and Education
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Logic Based Reasoning in
Medical AI Systems
Logic - the study of correct inference, of what follows from what
Logic in medical AI formalised as symbolic modes of reasoning
manipulating symbolic representations of facts and medical domain
knowledge
Stronger AI
Weak AI
Computerised
guidelines
Autonomous
agent Systems
Is “stronger” AI desirable let alone achievable ?
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Logic Based Reasoning in
Medical AI Systems
Symbolic logical representation
of knowledge
- Facts (patient data)
- Rules (medical knowledge)
+
Rules of Inference
e.g


Conclusions/Inference:
Control
- the way the world is
(beliefs)
abductive/deductive
- what one ought to do
(actions)
backward/forward

Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Inferring conclusions about the
way the world is
disease(peter,
myo_infarct)
disease(P,myo_infarct) 
symptom(P,short_breath)
symptom(peter,
short_breath)
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Inferring conclusions about the
way the world is
symptom(peter,
abnorm_ecg)
patient
investigation
disease(P,myo_infarct) 
symptom(P,abnorm_ecg)
disease(peter,
myo_infarct)
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Inferring how one ought to act
(belief1,..beliefn, action
 effect ,
effect  goal)
b1,b2
b1,b2  b3
e
eg
b3  b4
b1,b2,b3,b4…
Logic, Argument and Medicine
b1,b2,b3,b4, a  e
Medical Thinking, London, 22-23 June 2006
Inferring how one ought to act
(belief1,..beliefn, action  effect
effect  goal)
myo_infarct , aspirin 
reduced_platelet_adhesion
b1,b2
b1,b2  b3
b3  myo_infarct
reduced_platelet_adhesion
 prevent_blood_clotting
gi_bleed
gastritis , aspirin 
gi_bleed
gastritis
myo_infarct
myo_infarct , chlopidogrel 
reduced_platelet_adhesion
Logic, Argument and Medicine
reduced_platelet_adhesion 
prevent_blood_clotting
Medical Thinking, London, 22-23 June 2006
Logic-based Reasoning in
Medical Applications
Expert and Decision Support Systems for :
• Diagnostic Assessment (e.g., MYCIN, EMYCIN)
• Risk Assessment (e.g., RAGS)
• Therapy Planning and Critiquing (ONCOCIN, CAPSULE,
DAT)
• Decision Support embedded in computerised guidelines (e.g.,
ASBRU, PROforma based applications,…)
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Current and Future Directions –
Argumentation and Medicine
Argumentation theory, or argumentation, is the science of
effective civil debate or dialogue
Potential advantages of argumentation in medical AI
• Argumentation based Decision Support
• Communication of information from healthcare workers to patients
• Medical Education
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
What is an Argument (1) ?
Informally: a reasoned justification for a claim
Formal logical terms: conclusion (claim) and its logical proof (reasoned
justification)
An argument claiming b1 is the
case
b1 because of b2 and b3, and b3
because of b4, and b2 and b4
{b2,b4, b4b3, b2,b3 b1} : b1
Logic, Argument and Medicine
An argument for doing action a
action a should be executed
since given that b1 and b2
are the case, then a will result
in e being the case, which will
realise the desired goal g
Medical Thinking, London, 22-23 June 2006
What is an Argument (2) ?
Influential Toulmin argument schema:
Data
Claim , Qualifier
Warrant
Backing
myo_infarct
aspirin , 0.7
myo_infarct , aspirin 
reduced_platelet_adhesion
 prevent_blood_clotting
Clinical trial A
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Logical models of
Argumentation (1)
Conflict of opinion inevitable  arguments for and against competing
claims as to what is the case and what one ought to do
Logical accounts of argumentation for evaluating the winning arguments
m_i
aspirin, 0.7
myo_infarct , aspirin 
reduced_platelet_adhesion
 prevent_blood_clotting
Clinical trial A
Logic, Argument and Medicine
m_i
chlop, 0.5
myo_infarct , chlop 
reduced_platelet_adhesion
 prevent_blood_clotting
Clinical trial B
Medical Thinking, London, 22-23 June 2006
Logical models of
Argumentation (2)
Arguments interact in a network of conflict or “attack” relations
Apply a “calculus of opposition” to determine the winning arguments
chlo 0.5
Logic, Argument and Medicine
asp 0.7
gi_bleed
Medical Thinking, London, 22-23 June 2006
Proposition:
 |- decision_value(invade iraq, wrong) iff
 w s.t. w |= safe(X)  (|X| > |Y|)
PROOF : The complete-justified arguments of  are the same as in the
grounded extension [8]. Hence, we show that the grounded extension of  is a subset of the
grounded extension of ’. Dung makes use of iterative application of the operator F (in def.2)
F0 = ;, Fi+1 = {A 2 Args|A is collectively defended by Fi} - to show (if Args is finite) that
the grounded extension is given by S1 i=0(Fi).
Let G = F where G applies to AF0 and F to AF. We need to show that if A 2 Fi then A 2 Gi:
- i = 1: F1 = F(F0) contains arguments A that are not attacked/defeated, and since (by def.8-3) R0 R, then A 2 G1. (1)
- For i > 1, to show A 2 Gi we need to show that for any A 2 Fi: (B,A) 2 R and
(hence, given the definition of ‘collectively defend’ in def.2) 9C.C 2 Fi−1 and (C,B) 2 R, and
(B,A) 2 R0, implies 9C0.C0 2 Gi−1 and (C0,B) 2 R0 (2)
Assume (B,A) 2 R, 9C.C 2 Fi−1 and (C,B) 2 R, (B,A) 2 R0:
– i = 2 (F2 = F(F1)): We have 9C.C 2 F1 and by (1) C 2 G1, and since (C,B) 2 R and
¬9D s.t. (D,C) 2 R, then by definition 8-1) (C,B) 2 R0
Inductive hypothesis (IH): (2) holds for A 2 Fj j < i
– i > 2: Suppose (B,C) /2 R. Then by definition 8-1), (C,B) 2 R0, and by IH C 2 Gi−1.Suppose (B,C) 2 R and (C,B) /2 R0. By
assumption of (C,B) 2 R and definition 8-2), (B,C) 2 R0. By IH, C 2 Gi−1 and we can substitute C for A in (2). We have (B,C) 2 R
and (hence)
9C00. C00 2 Fi−2 and (C00,B) 2 R, and (B,C) 2 R0 and so 9C0. C0 2 Gi−2 and (C0,B) 2 R0.
Argumentation based Decision
Support – Argument as Explanation
RAGs (Risk Assessment in Genetics)
For use by doctors advising people with a family history of cancer
Makes use of weighted rules to formulate arguments for and against a person
belonging to given category of risk of being genetically predisposed to cancer
e.g., If person has 2 or more first-degree relatives diagnosed with breast cancer and both
relatives were diagnosed under the age of 40 then this is an argument for person being at
strong risk for genetic predisposition to the disease
Identical to classification by a statistical risk assessment package
Structuring and presentation of information as arguments represents
clear and intuitive way of communicating information to patients
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Argumentation for Consumers of
Healthcare
(AAAI Spring Symposium, March 2006, Stanford)
Enhancing the quality of doctor-patient communication by structuring
and presentation of knowledge in the form of arguments and their
conflict based interactions
Persuasive argumentation to change health-related behaviour
Patient Tailored Explanation
Lay orientated explanation of conflicting views in the medical
literature
Negotiation with Patients about treatment regimes
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Argumentation based
Collaborative Decision Making –
the CARREL project
CARREL framework developed at the University of
Catalonia for managing the human organ and tissue
transplant process
However, many organs potentially available for
transplantation are discarded (not extracted)
In Catalonia (a world leader in transplantation) 15 % livers 20%
kidneys 60% hearts 85% kidneys 95% pancreas are
discarded
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Argumentation based
Collaborative Decision Making –
the CARREL project
Potential
Donor
Detect
Donor Agent
No-viable
Discard
Viable /offer
CARREL
Recipient Agent 3
Recipient Agent 2
Recipient Agent 1
Argumentation based
Collaborative Decision Making –
the CARREL project
Current assignment ignores possibility of difference of opinion, e.g.,
- history of smoking implies non-viable
- smoking history but no history of COPD implies viable
Hence CARREL is being extended to allow recipient agents and donor
agents to argue over the viability of an organ
Winning argument for viability means that organ will be transplanted
rather than discarded
Work being undertaken as part of the ASPIC* project
*ASPIC (Argumentation Services with Integrated Components) - www.argumentation.org
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Potential
Donor
Detect
The Organ is non-viable
Because…
DAi
Transplant
Coordinator
The Organ is viable
Because…
DAi
CARREL
RA1
MA
RA1
RA2
Transplant
Unit
Transplant
Unit
Transplantado
RAn
Transplant
Unit
Argumentation based
Collaborative Decision Making –
the CARREL project
Mediator agent directs agents in dialogical exchange of arguments by
referencing 40 + schemes and critical questions
Schemes and critical questions identify possible challenges and
counter-arguments at each stage in the dialogue
Schemes and critical questions are template representations of
arguments and their interactions, for specialisation when arguing
about a particular case
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Argumentation based
Collaborative Decision Making –
the CARREL project
Non-Viability scheme:
Donor jDofoforgan
organkidney
O had had
condition
sve C
whichsve
And
is aiscontraindication
a contraindication
forfor
donating kidney
O
Therefore, organ
kidneyOisisnon-viable.
non-viable.
Disease
DiseaseTransfer
TransferContraindication
ContraindicationScheme:
Scheme:
Transplanting
Transplantingkidney
O fromfrom
D with
j with
condition
conditionsve
C leads
leads
to to
recipient
recipient
Rm
having
having
E,svi,
which
whichisisharmful
harmful
Therefore
Thereforesve
C isisa acontraindication
contraindication
Logic, Argument and Medicine
Is it the case that acondition
history of
C sve
is a is a
contraindication for donating O ?
kidney?
Action Prevention scheme
action
on m
prevents sve
Actionpencillin
Prevention
scheme
leading
sviRinprevents
m, and C
pencillin
Action Atoon
leadingisto E
intended
in R, and A is intended
VS(x,kidney,y)
Argument Schemes
And
Critical Questions
NVS(x,kidney,sve)
DAi
NVS_CQ2
NVS_CQ1
Deliberation
DDTS(x,sve,y,svi)
PAS(y,blood_samp,sve+)
RCAPS(teicoplanin,y,sve,x,svi)
RAj
RCAPS(penicillin,y, sve, x,svi)
RCACS(penicillin,y,pen_aller, sve, x,svi)
MA
VS(x,kidney,y)
Argument Schemes
And
Critical Questions
NVS(x,kidney,sve)
DAi
NVS_CQ2
NVS_CQ1
Deliberation
DDTS(x,sve,y,svi)
PAS(y,blood_samp,sve+)
RCAPS(teicoplanin,y,sve,x,svi)
RAj
RCAPS(penicillin,y, sve, x,svi)
RCACS(penicillin,y,pen_aller, sve, x,svi)
MA
Benefits
• Reduce disparity between supply and demand
• Schemes and critical questions can be instantiated by:
- arguments in natural language by human physicians (weaker AI) –
physicians thus directed to exploring all possible line of reasoning /
argument in a rigorous manner that does not compromise patient
safety
- arguments constructed in a logic programming language by
computerised donor and recipient agents (stronger AI)
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Benefits
• Educating medical professionals – evidence suggesting that the way
physicians reason follows from the way they have been educated
- Difficult to teach decision analysis techniques
- Argumentation is a familiar way of reasoning
- Scheme and critical question approach encourages comprehensive and
rigorous deliberation in a natural and intuitive way
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006
Conclusions
• Review of uses of logic in medical reasoning about what to believe and
how to act  logic based models of argument
• Applications of argumentation theory in the medical domain:
- Decision making
- Communication of health information
- Education
• Argumentation theory gaining ground in the AI community – parallel
development of memetics
Logic, Argument and Medicine
Medical Thinking, London, 22-23 June 2006